As methods for creating organic molecular thin films, a spin-coating method, an electrolytic polymerization method, a vapor deposition method, a vapor deposition polymerization method and the like are conventionally used. As a method for forming an alignment layer, the Langmuir-Blodgett (LB) method is well known. This method is performed as follows. Amphiphilic molecules are dissolved in a volatile organic solvent to be developed on a gas-liquid interface. After the solvent is vaporized, the resultant substance is compressed. The resultant monomolecular layer is transferred to a solid substrate. With this method, the number of the thin film layers and the order of lamination can be controlled. However, this method is only applicable to molecules which can be developed on a water surface as a monomolecular layer and thus is only effective for amphiphilic molecules, which are water-insoluble. The LB method is not efficient because the equipment to be used is expensive and cannot be easily handled.
A technology has been established for forming a self-assembled monolayer (SAM) including organic molecules regularly and stably aligned on a surface of a metal material such as gold or platinum, or a surface of an inorganic material such as silicon, silica or glass. Features of this technology are that the monolayer is strongly bonded to the substrate and so is stable, and the monolayer can be formed at low cost and in a simple manner without using any special equipment by merely immersing the substrate in a solution. In addition, this technology is applicable to a substrate having a complicated shape. This technology is attracting attention as, for example, a nanotechnology for constructing a pattern of organic molecules on an ultrafine pattern formed by a lithography technology(4).
An attempt is progressing to construct a three-dimensional structure in a bottom-up manner by laminating molecules on a two-dimensional plane by, for example, a layer-by-layer (LbL) method using electrostatic interaction of polyelectrolytes. This lamination method is based on the following principle. A substrate surface is immersed in a polyelectrolyte solution having the opposite charge to that of the substrate surface, so that one layer of the polyelectrolyte adsorbs to the substrate surface by electrostatic interaction. At this point, the substrate surface is newly charged oppositely by the excessive charges of the adsorbing polyelectrolyte. Next, one layer of the polyelectrolyte having the opposite charge to that of the polyelectrolyte layer already adsorbing is caused to adsorb to the surface. By repeating this process, a multi-layer structure controlled to have an arbitrary thickness can be formed. For example, it has been reported that an enzyme is immobilized, by electrostatic interaction, on a structure obtained by the LbL method, for the purpose of developing new molecular devices including enzyme reactors, biosensors and light emitting devices(1), (2). This method allows a three-dimensional structure to be prepared in a simple manner without using any special equipment and so is suitable to immobilize molecules of proteins or the like which may become denatured. In recent years, a method wherein a structure is obtained by forming a structure obtained through an LbL method atop a nonionic sacrificial film and then the sacrificial film is dissolved has been proposed(5). A technology for forming, atop a SAM, a structure obtained through an LbL method and then transferring the structure to a support film has also been reported(6).
The present inventors previously submitted a thin film polymer structure of arbitrary shape and preparation method therefor(3). For example, after forming a self-assembled monolayer on a round gold substrate body and subsequently adsorbing and crosslinking albumin thereto, the round albumin polymer thin film is easily caused to exfoliate from the gold substrate body through surfactant processing.
It is known that a hollow structure having a hollow of the shape of the mold can be obtained by forming a polyelectrolyte complex on the surface of a mold formed of an inorganic or metal microparticle or cell and then dissolving the mold(7). As the microparticle forming the mold, silica, latex bead, melamine resin or the like is used. The mold is dissolved by HF (hydrogen fluoride), an organic solvent, an acid or the like. There is no problem where a spherical microparticle is used as a mold, but a mold having a complicated shape is highly precise and thus is expensive like a printing plate or a plastic mold. Therefore, this method is usable only when the mold is stable and reusable. Since the above-described structures are formed in a bottom-up manner from the substrate, the surface of such a structure in contact with the substrate is not modified even after the structure is freed from the substrate.
There are no reports related to a method for modifying the surface in contact with the substrate for a structure obtained by existing nanotechnology. Also, a method whereby the face and reverse face of a thin film polymer structure in a dispersion state are easily and reliably modified with separate functional molecules is not known.